load cal says, heat loss of 64,000btu and 34,000 of heat gain. what would be the recommended sizing based on this for a split system, how many tons a/c and btus of gas heat?
in reguards to a/c tons what are the guidelines for the number of tons -vs- amount heat gain.(15,000=1ton, 20,000=2ton)?

06-12-2005, 07:42 PM

cem-bsee

you will now have to check each product for specific capacities -- be sure to understand what the criteria was for the rating -- what ambient/ outdoor temp

06-12-2005, 11:55 PM

beenthere

12,000 = 1 ton.

So it would appear that a 3 ton a/c, and a 80,000 input 80% furnace may do your house.

06-13-2005, 12:55 AM

Irishmist

fishin: Just curious. I appreciate your initiative in determining what size your home is calling for both in heating and in cooling. Are these the first steps in a do-it-yourself project, or are you going to have a contractor come in and provide you with a proposal?

Ideally, if your load is 34,000 btu for the cooling, you would want to come up with a 'match' between indoor and outdoor unit that gets you as close as possible to that number for the maximum efficiency. for example: you might find a "3" ton condensing unit when matched with a particular "3" ton coil, yields a cooling capacity of 33,500 btus. That would be a good match for your needs.

Also, keep in mind, that the recommendation provided you on an 80% afue furnace would not be the same as on a 90% afue furnace. That is, if your heating load was 64,000 btu, then the 80,000 is probably correct using an 80% furnace. However, to meet the same load using a 90% furnace, the btu input rating would be about 71,000, ideally.

06-13-2005, 08:03 PM

fishin

this is new construction, with a 90% VS furnace. contractor feels a/c should be sized up to 3.5 ton and 100,000 btus would be needed to push that much a/c.(i don't know any thing about that). my thinking based on the load cal. is 3.0 ton and 75,000 btus. can't an oversized furnace short cycle like an oversized a/c? as for the coils the one being used can be used with a 2 ton to a 3.5 ton compressor by changing the pin settings.

06-13-2005, 08:35 PM

beenthere

An over sized furnace will short cycle and use more fuel.

Don't let them over size your equipment, you'll be the one paying the price for years to come.

06-13-2005, 08:56 PM

Panama

Quote:

Originally posted by beenthere An over sized furnace will short cycle and use more fuel.

Not according to ACCA Manual S (1995). Manual S has a graph in Appendix 4 that shows negligible loss in efficiency if a modern furnace (AFUE > 75%) is oversized up to 5 times the heating load.

06-13-2005, 09:45 PM

beenthere

I seen that some years ago, and still don't beleive it.

06-13-2005, 10:16 PM

dan sw fl

Load & EQ Selection

Quote:

Originally posted by fishin this is new construction, with a 90% VS furnace. contractor feels a/c should be sized up to 3.5 ton and 100,000 btus would be needed to push that much a/c.(i don't know any thing about that). my thinking based on the load cal. is 3.0 ton and 75,000 btus. can't an oversized furnace short cycle like an oversized a/c? as for the coils the one being used can be used with a 2 ton to a 3.5 ton compressor by changing the pin settings.